Sect. II. RATE OF GROWTH. 97 



siderable thickness : but the subject has not, I believe, 

 been viewed in the proper light. 



That masses of considerable thickness have been 

 formed by the growth of coral, may be inferred with 

 certainty from the following facts. In the deep 

 lagroons of Peros Banhos and of the Great Chagos 

 bank, there are, as already described, small steep- 

 sided knolls covered with living coral. There are 

 similar knolls in the southern Maldiva atolls, some of 

 which, as Captain Moresby assures me, are less than a 

 hundred yards in diameter, and rise to the surface 

 from a depth of between 250 and 300 feet. Con- 

 sidering their number, form, and position, it would be 

 preposterous to suppose that they are based on pin- 

 nacles of rock, or on isolated cones of sediment. As 

 no kind of living coral grows above the height of a 

 few feet, we are compelled to suppose that these knolls 

 have been formed by the successive growth and death 

 of many individuals, — first one being broken off or 

 killed by some accident, and then another, and one set 

 of species being replaced by another set with different 

 habits, as the reef rose nearer the surface, or as other 

 changes supervened. The spaces between the corals 

 would become filled up- with fragments and sand, and 

 such matter would probably soon be consolidated, for 

 we learn from Lieut. Nelson's 1 observations at Bermuda 

 that a process of this kind takes place beneath water, 

 without the aid of evaporation. In reefs, also, of the 

 barrier class, we may feel sure, as I have shown, that 



1 Zoological Transactions, vol. v. p. 113. 

 H 



